1. Field of the Invention
The present invention relates to a communication interface in which a data-transmission rate (hereinafter referred to as a “data rate”) is variable and a cable to be used is defined as in a communication interface based on the IEEE 1394 standard, and in particular, to a technique for performing data communication with multi-purpose cables such as optical-fiber cables, UTP (unshielded twisted pair) cables and STP (shielded twisted pair) cables.
2. Description of the Related Art
A system in which electronic apparatuses such as a digital-video tape recorder, a digital television receiver, and a personal computer are connected by the IEEE 1394 (hereinafter referred to as the “1394”) serial bus, and a digital-video signal, a digital-audio signal, a control signal and so forth are communicated among the electronic apparatuses is considered.
In the cable connecting the adjacent apparatuses in this system there are provided two pairs of twisted pair cables. One pair of cables is used to transmit data, while another pair of cables is used to transmit strobes. The data is coded by the DS (data strobe) coding method, and is transmitted.
In addition, a Tp bias signal is output to the one pair of twisted pair cables. When the Tp bias signal is detected by one apparatus connected by the 1394 cable, the apparatus having detected the bias signal become aware of its being connected to another apparatus, and resets the bus. When the bus has been reset, physical addresses are automatically assigned to the respective apparatuses. When a digital-video signal or the like is transmitted, transmission of the signal is started after performing acquisition of a necessary band and channel.
A signal for notifying another apparatus of one apparatus's data rate is transmitted to the other pair of twisted pair cables. The apparatuses directly connected by the twisted pair cables are capable of knowing each other's data rate.
As described above, conventionally, a cable defined by the 1394 (hereinafter referred to as a “1394 cable”) is needed to realize communication via the 1394 serial bus (hereinafter referred to as the “1394 communication”).